The present invention generally pertains to solar energy collection and is particularly directed toward improving solar collector panel design by increasing the thermal efficiency of the panel.
A typical solar collector panel includes a collector plate for absorbing radiant heat; and a plurality of pipes in an array fastened to the surface of the collector plate for transporting a fluid for conducting heat energy from the solar collector plate.
In the design of solar collector panels used for swimming pool heating, space heating, and other heating and cooling applications, it is desirable that optimum efficiency be attained so as to reduce the initial cost of installation by reducing the panel area required for a given installation. The thermal efficiency of a solar collector panel depends primarily upon its capacity for transferring heat absorbed by the collector plate into the fluid through direct heat conduction.
Most solar collector panels presently being manufactured are not optimally efficient in conducting heat from the collector plate to the fluid. Typically the sheet stock for the collector plate is shaped to form semicircular channels into which the pipes are fitted. Because of the forming requirement, the sheet stock that is used is usually too thin to provide good lateral heat transfer from all parts of the collector plate to the pipes, thereby greatly reducing the operating efficiency. Also, machine forming of semicircular channels usually cannot be accomplished to the accuracy required for the close mating contact with the pipes required for efficient heat conduction.
The importance of achieving optimum thermal conductivity in a solar collector panel can be understood by examining the general equation for solar collector efficiency, which is: ##EQU1## Where: N = efficiency
F.sub.r =collector plate heat-removal efficiency factor PA1 .alpha..tau.= the averaged product of the collector plates' solar absorptance and the transmittance of the glazing cover PA1 U.sub.l = collector overall heat-loss factor PA1 Ti = inlet water temperature PA1 Ta = ambient collector temperature PA1 Qi = received solar radiation
The three most important considerations in collector panel design involve the factors of F.sub.R, .alpha..tau. and U.sub.L. The parameter .alpha..tau. is affected by the choice of the glazing material and collector plate absorber surface. Insulation properties of the collector panel govern the U.sub.L factor. The most neglected design factor in many of the current solar panels being marketed is that of F.sub.R.
The collector plate heat-removal efficiency factor F.sub.R, in effect, represents the thermal conductivity of the panels' heat-gathering apparatus. Efficient absorber surfaces, glazing materials and insulating materials are readily available and are employed in most collector designs. However, the heat-removal efficiency factor (F.sub.R) is not as a rule given prime consideration. The object of this invention is to maximize collector thermal conductivity (the F.sub.R factor) and thereby increase thermal efficiency.